As concerning the power supply device for all electronic products, except the performance has to meet the requirements of the power supply products, the protection measures of the power supply, such as over voltage protection, over current protection, over temperature protection. Once the electronic product fails, such as the short circuit at the input side or the open circuit at the output side in the electronic product occurs, the output voltage of the power supply must be turned off to protect the power device and the output side device from being burned. Otherwise, it may cause further damage to the electronic product or even cause the operator's electric shock and the fire phenomena, therefore, the over current protection function of the switching power supply must be perfect.
In the existing power circuit design, the resistor is generally used for the over current protection. However, when the over current protection circuit design of a high power supply or an ultra high power supply adopts an over current protection by a resistor, it may cause the resistor to burn out due to the over power and to cause a fire, which is urgent to be improved.